CVE-2026-77587: torproject tor Improper Update of Reference Count
CVSS: 7.5v3.1HighAnalyzed
AliasesUBUNTU-CVE-2026-77587DEBIAN-CVE-2026-77587
Published 20-08-2026Last modified 25-08-2026
Vulnerability summary
CVE-2026-77587 is a high (CVSS 7.5) Improper Update of Reference Count vulnerability in torproject tor. EPSS estimates a 0.40% chance of exploitation in the next 30 days, higher than 33.3% of scored vulnerabilities.
CVSS score
7.5/10
010
High · v3.1 (NVD)EPSS score
0.40%
0%100%
Low · +0.17 pp in 30 daysKEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded
Advisory lineage
Upstream 0 · Downstream 3 · Related 2Timeline
- 20-08-2026PublishedVulnerability first disclosed.
- 25-08-2026Last modifiedVulnerability information updated.
Description
Tor before 0.4.9.11 is prone to a use-after-free (and potential double free) of a conflux object when a recovery leg revives a conflux set whose last linked leg has already been closed. A malicious exit node could use this to crash a client. This is TROVE-2026-026.
CVSS metrics
4 scores · 4 sources · 1 versionHigh 7.5Preferred score · NVD (NIST)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HSources4 sources · 5.9–7.5
- CVE.orgCNA5.9MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:HDiffers
- OSV · UbuntuEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- OSV · DebianEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS trend
Probability
0.40%
Chance of exploitation in the next 30 days
Percentile
33%
Versus all other CVEs
30-day change
+0.17 pp
From 0.23% on 19-09-2026
19-09-202619-10-2026
EPSS score0.40%
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root cause- CWE-911Improper Update of Reference CountThe product uses a reference count to manage a resource, but it does not update or incorrectly updates the reference count.
- CWE-416Use After FreeThe product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.
Affected systems
Debian1 product
- tor< 0.4.9.11-0+deb12u1 | < 0.4.9.11-0+deb13u1 | < 0.4.9.11-1
Torproject1 product
- tor≥ 0.4.8.1-alpha, < 0.4.9.11 | < 0.4.9.11
Ubuntu1 product
- torAll versions (No fix recorded)
3 vendors · 3 products
References
5 links- gitlab.torproject.org/tpo/core/tor/-/raw/tor-0.4.9.11/ChangeLogPermissions RequiredRelease NotesVendor Advisory
